JPH04365264A - Original reader - Google Patents

Abstract

PURPOSE:To obtain the original reader which can correct the output level of a photoelectric conversion element at low cost with high accuracy when a light source is turned off. CONSTITUTION:At the original reader equipped with a subtracter 206 to sample the dark time output signal of a photoelectric conversion array 107 after the A/D conversion of an A/D converter 205, to store the signal in a memory 207 over the image read period of one frame, to read this dark time output level and to subtract it from an image signal and a peak detection circuit 208 to detect the maximum value of the output signal from the photoelectric conversion element array 107 in the case of reading a reference density board before reading the original, control signals P1-P4 outputted from the peak detection circuit 208 in the case of sampling the dark time output signal of the photoelectric conversion element array 107 are made equal to control signals P1-P4 set by reading the reference density board when reading the original last time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to document reading devices such as digital copying machines and facsimiles, and to improvements in correcting the output level of photoelectric conversion elements during dark times.

0002

[Prior Art] Conventionally, halogen lamps, fluorescent lamps, LED arrays, etc. have been used as light sources for document scanners, but illuminance variations due to individual differences, temperature changes, changes over time, etc.
In order to absorb the attenuation difference between optical system components, the sensitivity difference between individual photoelectric conversion elements, etc., and convert the output of the photoelectric conversion element into A/D in the most efficient manner and with a large dynamic range, Broadly speaking, the following two methods are known. (1) The light source is dimmed so that the output of the photoelectric conversion element when reading the reference white plate becomes a predetermined level. (2) A variable gain amplifier or the like is provided in the image processing circuit so that the output of the photoelectric conversion element when reading the reference white plate is at a predetermined level.

However, if the light source is dimmed, the cost will increase significantly, and the dimming time required will increase the reading time. A method of correcting this is used. By the way, photoelectric conversion elements have a certain level of output even in the dark, and this reduces the stability and gradation of the image output, so image signals are corrected using various methods. In terms of accuracy, the best method is to store all pixel outputs of the photoelectric conversion element array as digital values when reading the reference black plate, and then correct them when reading the original.

However, when the reference white plate and the reference black plate are placed adjacent to each other, the output of the photoelectric conversion element is affected by the flare of the light source, and the predetermined white and black levels are not achieved. It is necessary to arrange both of them with a sufficient distance in the traveling direction of the traveling body, which results in an increase in the size of the device, an increase in cost, and an increase in reading time due to an increase in the run-up distance of the traveling body. In order to prevent such inconveniences, a method has been proposed in which the output of the photoelectric conversion element before the light source is turned on is sampled as a reference black. A conventional example of this type of technology is JP-A-62-
73869, JP-A-62-235871, and the like.

FIG. 16 is a schematic diagram of the optical system of a conventional document reading device (scanner). In the figure, 10
1 is a contact glass, 102 is a reference white plate, 103 is a light source lamp, 104 is a first mirror, 105a is a second mirror, 105b is a third mirror, 106 is a lens, and 107 is a CCD.

FIG. 1 is a schematic block diagram of the image signal processing system of the above-mentioned document reading device.
By extracting only the signal part, CCD1
07 reset noise is removed. A variable gain amplifier (GC.Amp) 204 has a configuration as shown in FIG. The gain can be varied from 1 to 15 values using the four control signals P4 to P1. 205 is an A/D converter (ADC) that converts the output of the variable gain amplifier 204 into 6-bit digital data. A subtracter 206 performs dark output correction by subtracting the dark output from the document reading output. Reference numeral 207 denotes a dark output storage memory, which performs the operation of writing the output values of all pixels of the CCD to the corresponding address of the memory 207 when the light source lamp 103 is turned off, and writes the output values of all the pixels of the CCD to the corresponding address of the memory 207 when the light source lamp 103 is turned on.
The dark output is read from the address corresponding to the output pixel of D107. A peak detection circuit 208 detects the highest value in one line of CCD output. Usually, a reference gain is given to the variable gain amplifier 204 (1, 1,
1, 0) are output as the control signals P1 to P4, but after the light source is turned on, the upper 4 bits of the 6 bits of the peak value detected when reading the reference white plate 102 are output as the control signal, and the original is read. Hold this until finished.

For example, 42 in decimal system (1,0 in binary system)
, 1, 0, 1, 0) is obtained, (1, 0, 1, 0) is output as the control signals P1 to P4. As a result, the peak value 42 is 42÷(15/14)×(15/10)=58.8, which is 5 from the gain table in Figure 18.
9, and the conversion width of the 6-bit A/D converter 205 can be used effectively for subsequent document reading. FIG. 19 shows an operation timing chart of the document reading device. Gn
-1 is the gain when reading the previous original, G0 is the reference gain (P4 to P0 = 1, 1, 1, 0), and Gn is the gain when reading the current original.

[0008]

[Problem to be Solved by the Invention] By the way, the value sampled by the variable gain amplifier 204 at the reference gain of the dark output for a certain pixel of the CCD 107 before the light source is turned on is 1.
If it is 2 in decimal notation, the original dark output under the modified gain when reading the original is 2 ÷ (15/14) x (15/10) ≒ 3, which is the dark output value read from the memory 207. 2 had a problem that could not be completely corrected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a document reading device that can correct the output level of a photoelectric conversion element at low cost and with high precision when the light source is turned off.

0010

[Means for solving the problem] The above purpose is to sample the image signal output by the photoelectric conversion element when the light source is turned off,
A/D converting means for storing the image signal in a storage means over the image reading period of one frame, and correcting means for correcting the image signal output from the photoelectric conversion element based on the level of the output signal from the storage means; A document reading device comprising a setting means for setting the output signal level of the photoelectric conversion element to a predetermined level based on the output signal level of the photoelectric conversion element when reading a reference density plate prior to reading the document, A first step in which the setting level of the setting means when sampling the output signal of the photoelectric conversion element when the light source is turned off is the same as the level set by the setting means by reading the reference density plate during the previous document reading; This is accomplished by the following means. In addition, the above purpose is to sample the image signal output by the photoelectric conversion element when the light source is turned off, and convert it into an A/D signal.
stored in a storage means over an image reading period of the frame;
a correction means for correcting the image signal output from the photoelectric conversion element based on the level of the output signal from the storage means; and an output signal level of the photoelectric conversion element when reading the reference density plate prior to reading the original. In an image reading device having a setting means for setting the output signal level of the photoelectric conversion element to a predetermined level, and a temperature measuring means for measuring the tube surface temperature of the light source lamp, The setting level of the setting means to be set when reading the reference density plate is predicted in advance based on the tube surface temperature information, and the setting level is used when sampling the output signal of the photoelectric conversion element when the photoelectric conversion element is turned off. This is achieved by the second means of setting the setting level of the setting means. Furthermore, the above purpose is
The image signal output by the photoelectric conversion element when the light source is turned off is sampled, A/D converted, and stored in a storage means over the image reading period of one frame, and the photoelectric conversion element is a correction means for correcting an image signal output from the conversion element; and a predetermined output signal level of the photoelectric conversion element based on the output signal level of the photoelectric conversion element when reading a reference density plate prior to reading the original. When performing a continuous reading operation in an image reading device having a setting means for setting the level to a level of For the first time, the setting level of the setting means at the time is set by predicting in advance the setting level to be set when reading the reference concentration plate based on the tube surface temperature information from the temperature measuring means, and for the second and subsequent readings. The operation is achieved by a third means that sets the same level as the level set during the previous read operation.

[0011]

In the first means, the image signal output by the photoelectric conversion element when the light source is turned off is sampled, A/D converted, and then stored in the storage means over the image reading period of one frame. The correction means corrects the image signal read and output by the photoelectric conversion element based on the level of the image signal output from the storage means. On the other hand, the setting means sets the output level of the photoelectric conversion element to a predetermined level based on the output level obtained by reading the reference density plate with the photoelectric conversion element prior to document reading scanning. The setting level set by the setting means by reading the reference density plate with the photoelectric conversion element during the previous document reading is the same as the setting level of the setting means when sampling the image signal output by the photoelectric conversion element next time when the light source is turned off. be done. In the second means, the temperature measuring means measures the tube surface temperature of the light source lamp and transmits tube surface temperature information to the control means. Based on the tube surface temperature information, the control means reads the reference density plate with the photoelectric conversion element, predicts the setting level to be set by the setting means, and samples the image signal output by the photoelectric conversion element when the light source is turned off according to the setting level. do. In the third means, when performing continuous reading operations, the first reading is performed according to the setting level based on the prediction of the setting level described above, and from the second time onwards, the setting level is set by reading the reference density plate during the previous reading operation. Therefore, the image signal output by the photoelectric conversion element when the light source is turned off is sampled.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. Note that the same reference numerals are given to parts that are the same as or can be considered to be the same as in the conventional example, and redundant explanations will be omitted. First, a first embodiment having the same circuit configuration as the conventional example will be described. As mentioned above, although the illuminance of the light source lamp fluctuates due to changes over time and temperature dependence (particularly when fluorescent lamps are used), we focused on the fact that it is stable during each reading operation, and in this example, we The amplifier gain at the time of output sampling is set to the gain set at the previous reading, rather than the reference gain prepared for gain correction by reading the reference density plate.

Since illuminance fluctuations are gradual with respect to the document reading speed of the scanner, for example, if the current gain control signal is
4 ~ P0 = 10 (1, 0, 1, 0), the previous control signal was within ±1 with respect to 10, and if 9 (
1, 0, 0, 1), the dark output sampling value will be correctly corrected by 2÷(15/14)×(15/9)≈3. Figure 3 shows the timing chart in this case.
Shown below.

In this embodiment, the variable gain amplifier 20
4 (Fig. 17) was used to explain an example of converting the output of a photoelectric conversion element to an appropriate level.
This can be easily realized by converting the detected peak value and applying it as a conversion reference voltage of an A/D converter, or by frequency converting the detected peak value and varying the light accumulation time of the photoelectric conversion element. A schematic image processing block diagram of a modified example corresponding to each case is shown in FIGS. 2 and 3.

In FIG. 2, 209 is a D/A converter, which converts the peak value detected by the peak detection circuit 208 into a D/A converter.
The voltage is converted and applied to the A/D converter 205 as a conversion reference voltage.

In FIG. 3, a frequency converter 210 converts the frequency of the peak value detected by the peak detection circuit 208, thereby making the light accumulation time of the CCD 107 variable.

Next, a second embodiment will be described in which the illuminance of the light source lamp has dependence on the light source temperature. As mentioned above, we focused on the fact that when the light source is a fluorescent lamp, the illuminance varies depending on the tube surface temperature of the fluorescent lamp. The illuminance during the document reading operation is predicted before the light source is turned on based on the tube surface temperature - illuminance ratio data and the actual illuminance value when reading the reference white board at a certain tube surface temperature, and this predicted value is used to adjust the gain of the variable gain amplifier 204. (gain) and sample the dark output.

FIG. 8 is an external view of the main parts of the fluorescent lamp (light source lamp) 103, in which a temperature sensor (eg, thermistor, thermocouple) 30 is placed on the surface of the fluorescent lamp at a position that does not block the optical path.
1 to monitor the tube surface temperature.

FIG. 4 is a schematic block diagram of image signal processing, in which the control section 211 controls the variable gain amplifier 20 based on the tube surface temperature from the temperature sensor 301 and data from the peak detection circuit 208.
Control 4. FIG. 9 is a graph showing the tube surface temperature-illuminance ratio characteristics of a typical fluorescent lamp, and the control unit 211 converts such characteristics into data and stores it as discrete illuminance ratio data with respect to the tube surface temperature shown in FIG. are doing.

Next, the operation of the second embodiment will be described based on the flowcharts shown in FIGS. 11 to 13. FIG. 11 shows the sequence control after the power is turned on. First, the fluorescent lamp 103, the first mirror 104, the second mirror 105a, the third mirror 105b, etc. are returned to the home position (step 1; S1 Same below). At this time, a reference white plate 102 is placed at the reading start position on the optical path document placement surface. In S2 to S5, the peak value D0 of the light source illuminance data at the tube surface temperature T0 is collected and stored in the memory 207. In S6, the fluorescent lamp 103 is turned off and preparations are made to start reading the document.

FIGS. 12 and 13 show the subroutine of the reading operation. When the reading operation is started, the current tube surface temperature T is collected in S10 of FIG.
If the light source is currently turned on, how much illuminance will be obtained is predicted by calculation from the tube surface temperature - illuminance ratio data in FIG. 10 (S11), and the upper 4 bits are used as the gain of the variable gain amplifier 204 in S12 Set to . Under the setting of the gain that provides this predicted illuminance, the dark output is held in the memory 207 in S13, and a correction operation is performed. And S14~1
6, similarly to the conventional example, the gain of the variable gain amplifier 204 is set in accordance with the actual illuminance, and thereafter the document reading operation is performed as shown in FIG. 13 (S17), and when it is finished (S18
(YES) Turn off the light source in preparation for starting the next reading (S19)
, reference gain setting of variable gain amplifier 204 (S20), dark output sampling (S21), traveling body return (S2
Do 2).

Note that if the actual machine data collected in S2, S5, S10, and S16 is reflected and updated in the tube surface temperature-illumination ratio data in FIG. , it is also possible to cope with deterioration of light source characteristics over time.

FIG. 6 is a timing chart of the operation of the second embodiment, where Gne is the gain obtained by prediction, and Gne is the gain obtained by prediction.
0 is the reference gain, Gn-1 is the gain when reading the previous original, and Gn is the gain when reading the current original.

Finally, regarding a third embodiment in which a part of the operation of the second embodiment is changed, only the differences from the second embodiment will be described. As mentioned above, the illuminance fluctuation of the light source lamp is gradual compared to the time required for one document reading operation;
In addition, we focused on the fact that especially in the case of fluorescent lamps, the illumination intensity is largely dependent on the tube surface temperature, and in this embodiment, the illuminance is predicts the illuminance during document reading operation before the light source is turned on, based on the tube surface temperature-illuminance ratio data of the light source lamp stored in advance in the device and the actual illuminance value when reading a reference white board at a certain tube surface temperature. , the gain of the variable gain amplifier 204 is set based on this predicted value, and the dark output is sampled.

In addition, in the second and subsequent operations of a plurality of consecutive document readings, the dark output is sampled at the gain set at the time of reading the reference white board during the previous document reading.

FIGS. 14 and 15 are the second embodiment shown in FIG.
This is a flowchart of a reading start subroutine corresponding to the flowchart of FIG. 13, and the same processing steps as in the flowcharts of FIGS. 12 and 13 are given the same step numbers (S1, S2, etc.). To explain only the differences from the flowcharts in FIGS. 12 and 13, FIG.
After turning off the light source (S19), the dark output sampling mode is set (S23). Here, it is determined whether there is a next document reading operation (continuous reading or not) (S24), and if not, a reference gain is set in the variable gain amplifier 204 (S25), and the traveling body is returned to resume the operation. The process is terminated (S26).

If there is a next document reading operation, the traveling body is returned with the gain setting of the variable gain amplifier 204 unchanged at the time of document reading (S27), the process returns to S13, and the dark output is held in the memory 207 (S27). S13), hereinafter S14
Or in S19 and S24, the same operation as last time is performed. When the final document reading operation is completed, the series of operations ends through S25 and S26.

A timing chart in this case is shown in FIG. Gn e is the gain obtained by prediction, G0 is the reference gain, Gn is the gain when reading the original for the first time, Gn +
1 is the gain when reading the document for the second time, and Gn + 2 is the gain when reading the document for the third time.

[0029]

Effects of the Invention According to the invention described in claims 1 and 2,
By making the setting level of the setting means when sampling the output signal of the photoelectric conversion element when the light source is turned off to be the same as the level set by reading the reference density plate during the previous reading of the document, According to the invention described,
The setting level of the setting means to be set when reading the reference density plate is predicted in advance based on the light source lamp tube surface temperature information from the temperature measuring means, and the setting means is set when sampling the output signal of the photoelectric conversion element when the light source is turned off. By setting the level,
Furthermore, according to the invention as set forth in claim 6, when performing a continuous reading operation, the setting level of the setting means when sampling the output signal of the photoelectric conversion element when the light source is turned off is initially set to the tube surface temperature from the temperature measuring means. Based on the information, the setting level determined when reading the reference white board is predicted and set in advance, and the second and subsequent operations are set to the same setting level as the level determined during the previous reading operation. Since the setting of the photoelectric conversion element output level setting means can be almost the same as that when reading the original, accurate image signal output correction can be performed when the light source is turned off, so there is no increase in reading time, and high gradation and high precision can be achieved. It is possible to provide a document reading device of

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an image signal processing system of a document reading device according to a first embodiment of the invention of the present application.

FIG. 2 is a schematic block diagram of an image signal processing system of a document reading device according to a modification of the first embodiment.

FIG. 3 is a schematic block diagram of an image signal processing system of a document reading device according to a modification of the first embodiment.

FIG. 4 is a schematic block diagram of an image signal processing system of a document reading device according to a third embodiment.

FIG. 5 is a timing chart according to the first embodiment.

FIG. 6 is a timing chart according to a second embodiment.

FIG. 7 is a timing chart according to a third embodiment.

FIG. 8 is an external view of main parts of a fluorescent lamp.

FIG. 9 is a tube surface temperature-illuminance ratio characteristic diagram of a fluorescent lamp.

FIG. 10 is a chart showing the contents of tube surface temperature-illuminance ratio characteristic data of a fluorescent lamp.

FIG. 11 is a flowchart of a main routine when the power is turned on according to the second embodiment.

FIG. 12 is a flowchart of the first stage of a subroutine at the start of reading according to the second embodiment.

FIG. 13 is a flowchart of the latter part of a subroutine at the start of reading according to the second embodiment.

FIG. 14 is a flowchart of the first part of a subroutine at the start of reading according to the third embodiment.

FIG. 15 is a flowchart of the latter part of a subroutine at the start of reading according to the third embodiment.

FIG. 16 is a simplified configuration diagram of an optical system of a document reading device.

FIG. 17 is a configuration diagram of a variable gain amplifier.

FIG. 18 is a chart showing gain data of a variable gain amplifier.

FIG. 19 is a timing chart according to a conventional example.

[Explanation of symbols]

101 Contact glass 102 Standard white plate 103 Light source lamp 107 CCD 204 Variable gain amplifier 205 A/D converter 207 Memory 208 Peak detection circuit 209 D/A converter 210 Frequency converter 211 Control unit 301 Temperature sensor

Claims (6)

[Claims] 1. An image signal output by a photoelectric conversion element when the light source is turned off is sampled, A/D converted, and stored in a storage means over the image reading period of one frame, and the level of the output signal from the storage means is determined. a correction means for correcting the image signal output from the photoelectric conversion element based on the output signal level of the photoelectric conversion element based on the output signal level of the photoelectric conversion element when reading the reference density plate prior to reading the original; In an original reading device having a setting means for setting an output signal level to a predetermined level, the setting level of the setting means when sampling the output signal of the photoelectric conversion element when the light source is turned off is set to the level set by the setting means when sampling the output signal of the photoelectric conversion element when the light source is turned off. A document reading device characterized in that the level is set to be the same as the level set by the setting means by reading a reference density plate. 2. The setting means according to claim 1, wherein the setting means is a voltage applying means for applying a conversion reference voltage to the A/D converter, or a variable voltage applying means for variably amplifying the output signal of the photoelectric conversion element. A document reading device characterized in that it is a gain amplification means or a control means for controlling a charge accumulation time of the photoelectric conversion element. 3. The image signal output by the photoelectric conversion element when the light source is turned off is sampled, A/D converted, and stored in storage means over the image reading period of one frame, and the level of the output signal from this storage means is determined. a correction means for correcting the image signal output from the photoelectric conversion element based on the output signal level of the photoelectric conversion element based on the output signal level of the photoelectric conversion element when reading the reference density plate prior to reading the original; In an image reading device having a setting means for setting an output signal level to a predetermined level and a temperature measuring means for measuring a tube surface temperature of a light source lamp, the reference temperature is determined based on tube surface temperature information from the temperature measuring means. The setting level of the setting means that is set when reading the density plate is predicted in advance, and the setting level is used as the setting level of the setting means when sampling the output signal of the photoelectric conversion element when the photoelectric conversion element is turned off. Characteristic image reading device. 4. The advance prediction by the setting means includes reading tube surface temperature contrast intensity ratio characteristic data of the light source lamp stored in advance in the storage means and a reference density plate at a certain tube surface temperature. An image reading device characterized in that the image reading device is calculated based on an output value of the photoelectric conversion element when the photoelectric conversion element is detected. 5. In claim 3, the tube surface temperature contrast intensity ratio characteristic of the light source lamp is determined by the tube surface temperature measured by the temperature measuring means and the output of the photoelectric conversion element when reading the reference density plate. An image reading device characterized in that the image reading device is updated based on a value. 6. The image signal output by the photoelectric conversion element when the light source is turned off is sampled, A/D converted, and stored in storage means over the image reading period of one frame, and the level of the output signal from this storage means is determined. a correction means for correcting the image signal output from the photoelectric conversion element based on the output signal level of the photoelectric conversion element based on the output signal level of the photoelectric conversion element when reading the reference density plate prior to reading the original; In an image reading device having a setting means for setting the output signal level to a predetermined level and a temperature measuring means for measuring the tube surface temperature of the light source lamp, when performing a continuous reading operation, the photoelectric conversion when the light source is turned off is performed. The setting level of the setting means when sampling the output signal of the element is initially set by predicting in advance the setting level to be set when reading the reference concentration plate based on the tube surface temperature information from the temperature measuring means,
An image reading device characterized in that in a second and subsequent reading operations, the same set level as the level set in the previous reading operation is set.